the Total Fertility Rate

The total fertility rate, sometimes also called the fertility rate, absolute/potential natality, period total fertility rate or total period fertility rate of a population is the average number of children that would be born to a woman over her lifetime if:

Fertility is the natural capability to produce offspring.

Distilled Demographics: The Birth Rate by Population Reference Bureau

She were to experience the exact current age-specific fertility rates through her lifetime, and

Videographic: Are Asian fertility rates declining? by The Economist

She were to survive from birth through the end of her reproductive life.

It is obtained by summing the single-year age-specific rates at a given time.